I've been working on the final design for SWIFTWOOD's akas.
First I've moved the akas mounting positions. There were at 1/3 and 2/3 the length of the boat, just aft
of each mast, so I can run the stays and mount the leeboards.

With the greater width of the boat. I've decided that this is not enough separation. Since all three hulls
have square transoms I've move the aft aka all the way to the stern. I've moved the forward one ahead
of the bow. OK, doesn't this mess up leeboard placement? Your asking. Good question. But I'm also
going ahead with lifting hydrofoils, more of an assist. Always in the game plan to try it, but easier to do
now.

I'm going with a 4 poster design, 2 hydrofoils on each aka. These need to be as far apart as possible,
one of the reasons for moving the akas mounts. The rear foils will also be the boats rudders, actually the
supporting struts will be. This is like having twin leeboards on both amas. If I had no jib the rig would
be balanced by placing them and the stern and at the forward mast. Since I have a jib, the forward one
needs to move forward some what.

Hopefully this is all clear now.

I tossed around a lot of ideas for aka design, which I'll go over before I present the design I'm working
on.

Truss.
real strong and light, but a lot of windage, and not the most estetically appealing.

Wire stayed truss, like a bridge.
Real strong and light, like those seen on the Hobie Cat Tri-foiler. I like the look, but when I built a
prototype, it was difficult to setup, not good for a trailer sailor. It also lacked a certain inherit strength.
The beams need to be much stiffer than finally needed in order to setup the stays. It also need to be
braced on the top and the bottom. The structure would have been 5 feet tall!

This leads back to conventional beams, there are several types.
Round tubes.
They work, but are not efficient structurally, the load is parabolic, or efficient aerodynamically.
Round is actually worse that square.

Simple I-beams.
They work, but are not efficient structurally, the load is parabolic, or efficient aerodynamically.
If they are a foot tall each beam will present 20sqft perpendicular to motion.
The structural inefficiency can be rectified by tapering the beams, leaving a short profiles out at the amas
where it's more critical.

Open beams.
The top and bottom plates are full to take the load, but the web is opened up on some places to let
air/water pass through. This sound good, but the additional bracing to allow for web removal will rive
the weight up.

Box beams
Like an I beam but with webs are both ends. Once tapered they are very efficient structurally, but still
lack aerodynamics efficiency.

Airfoil
The most aerodynamic. But not the structurally efficient. Beam theory dictates that most of the structure
needs to be put as far away from the centroid as possible, and airfoil, or even an oval structure is just
the opposite! This is why carbon fiber is used in most of these designs. The skin thickness is varied so
that is it thicker at the top and bottom were the load is.
Also there's another problem airfoils need to be at a minimum 4 times in length as they are high. So for
a beam 18in high at the Vaka they need to be 6 feet long! This also explains the interest in wing akas!

D shaped beams.
These are a compromise between I beams and airfoils. Since the beams are so close to the water,
hitting a wave can cause a capsize. The streamlining of the forward part is more for wave impacts than
for aerodynamic efficiency, but it helps out a lot.

So which one did I pick?
Since weight is critical on my boat, I'm going with the D shaped taped akas, that will also have a
curved gull wing profile.

For construction I still want to use wood, but they will need to be reenforced with carbon fiber in order
to get the weight down. Ideally for me this will be on the inside so you can see all that pretty wood

There's two parts the flat back part, with can also serve as a backbone during the construction and the
curved forward piece.

I could strip plank the curved piece, the carbon fiber would then be laid up before the back is attached,
this would require some sort of shelf since you cannot tape the inside of the joint once the back is on.

Another option is to stick with plywood The shape could be formed by using a top and bottom piece to
form the curved piece. The top and bottom are first attached to the back piece forming a C channel
Both of these joints can be taped with carbon fiber instead of glass to get the I beam strength mentioned
above. The curve is now for by bending the top and bottom panels together, forming a sharp Vee
section to present to the waves. Since, once again, the inside cannot be taped a piece of wood will
need to be attached and tapered to the angle of the Vee, which is not constant.

The only question is whether or not the plywood can take all that compound bending, the akas will be curved as well as tapered

So what do you think?